Specifications

Telephone Interface 63

4.2.3.4 Signaling Byte

This section describes how DECvoice uses the signaling byte during a

module write operation (from module to TLI) and a module read operation

(from TLI to module).

Module Write Operation

The DTC04 module sends the signaling byte to the TLI to control the

output of the signaling pins on the 29C50 chip. Figure 4-2 shows how the

bits in the signaling byte correspond to the pins on the 29C50 chip.

MA-0566-88

Figure 4–2 Signaling Byte From the Module

The R1 signaling pin serves as a hook switch. When R1 is 0, the

telephone is off the hook. When R1 is 1, the telephone is on the hook.

R1 is used for answering the telephone and pulse dialing. DECvoice does

not use signaling pins R2, A, B, C, and D.

Module Read Operation

The TLI sends the signaling byte to the module to inform it of the state

of signaling pin X1 and which of pins A, B, C, and D are programmed to

transmit. Figure 4-3 shows how the bits in the signaling byte correspond

to the pins on the 29C50 chip.

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Figure 4–3 Signaling Byte to the Module

Signaling pin A is used for ring detection. Signaling pin X1 is used for

line current detection. DECvoice does not use pins B, C, and D. Signaling

pins labeled with a Z are undeﬁned.